CSCI-1200/lectures/optimization/gprof/README.md

# C++ Profiling with `gprof`

## What is `gprof`?
`gprof` is a GNU profiler that helps analyze where a program spends most of its execution time. It provides function call counts and execution time details.

## Installing `gprof`
```sh
sudo apt-get install binutils

Compiling a C++ Program for Profiling

To use gprof, compile your program with the -pg flag:

g++ -pg -o my_program my_program.cpp

Example C++ Program

Create a file my_program.cpp with the following code:

#include <iostream>
#include <chrono>
#include <thread>

void slowFunction() {
    std::this_thread::sleep_for(std::chrono::seconds(1));
}

void fastFunction() {
    for (volatile int i = 0; i < 1000000; ++i);
}

int main() {
    for (int i = 0; i < 5; ++i) slowFunction();
    for (int i = 100; i < 200; ++i) fastFunction();
    return 0;
}

Running and Profiling the Program

1. Compile the program:

   g++ -pg -o my_program my_program.cpp
   

2. Execute the program to generate gmon.out:

   ./my_program
   

3. Analyze the profiling data:

   gprof my_program gmon.out > profile.txt
   cat profile.txt
   

Understanding the Output

• Flat Profile: Shows execution time spent in each function.
• Call Graph: Displays function call relationships and their execution time.

Best Practices for Using gprof

• Use -O2 optimizations but avoid -O3, which may inline functions and reduce profiling accuracy.
• Profile with realistic input data to get meaningful results.
• Optimize the slowest functions first based on the profiling report.

Conclusion

gprof is a powerful tool for detecting performance bottlenecks in C++ programs. By identifying expensive functions, developers can make targeted optimizations.